Monoalkylxylenes by alkylation



Oct- 9. 1956 |;:A A. MCCAULAY ETAL 2,766,307

. MoNoALKYLxYLENEs BY ALKYLATION Filed Oct. 26, 1955 INVENToRs: David A. McCall/ay United States y* ,llatent O.

2,766,307 MONDALKYLXYLENES BY ALKYLATION David A. McCaulay, Chicago, lll., and Arthur P. Lien, Highland, Ind., assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application October 26, 1953, Serial No. 388,238 13 Claims. (Cl. 260-671) This application is a continuation-in-part of our copending application Serial No. 237,916, led July 21, 1951, now abandoned.

This invention relates to the preparation of monoalkylxylenes by the reaction of an olefin and xylene. More particularly, the invention relates to the preparation of ethylxylenes. Still more particularly the invention relates to the preparation of the symmetrical 1,3,5-ethylxylene.

The commercial polystyrene resins have the disability of a softening point lower than the boiling point of water. It is known that resins prepared from dimethylstyrene have a softening point higher than the boiling point of water. Ethylxylenes with an ortho arrangement of a methyl and the ethyl group dehydrogenate to methylindenes, which are very diicult toseparate from the dimethylstyrene. The methylindenes act as plasticizers' and lower the softening point of the polydmethylstyrene; the presence of more than about 6% of these contaminants lowers the softening point of the resin below the boiling point of water. In the prior art processes,

this undesirable ortho relationship between a methyl andv 4ll the alkyl group exists in the major portion of the ethylxylene product.

The development of the hydroperoxide synthesis for phenols has caused a large demand for substituted secondary alkylbenzenes. desired in order to permit the production of phenols of specific characteristics. 1,3,5-isopropylxylene is of particular interest in this synthesis.

It is an object of this invention to alkylate xylenes with olens to produce preferentially monoalkylxylenes, which contain predominantly 1,3 dimethyl- 5 alkylbenzene. Another object of our invention is to produce ethylxylenes containing a predominant amount of 1,3,5-ethylxylene by ethylating xylenes. Still another object is to prepare essentially pure 1,3,5-ethylxylene by ethylating xylenes. A further object is the preparation of 1,3,5-secondary alkylxylenes by alkylating xylene. A particular object is the preparation of 1,3,5-isopropylxylene. Yet another Essentially pure isomers are 2,766,307 `Patented Oct. 9, .1956

ice

object is the preparation of 1,3,5-tert-butyl'xylene. Other objects will be apparent in the detailed description.

It has been found that by the use of liquid HF-BFs catalyst under controlled conditions, each of the xylene isomers or mixtures thereof can be readily alkylated with ethylene, propylene, butene-l, butene-Z and isobutylene to produce ,preferentially monoalkylxylenes.

The feed to the process comprises any one of the three xylene isomers or mixtures thereof. In the presence of HF-BFS agent, olefins alkylate benzene and toluene very readily; therefore, the presence of more than appreciable amounts of benzene and toluene should be avoided.

The acid phase can dissolve a fair amount of parafns, for example, the'xylene feed may contain4 as much as 3 volume percent of paratiins without forming a separate hydrocarbon phase (when at least about 1 mol of BFa is present per mol of xylene charged). The presence of a hydrocarbon phase, i. e., railinate phase, is not desirable because some of the xylene is withdrawn from the acid phase and the yield of alkylxylene is decreased and the product distribution is shifted from the desired maximum of 1,3,5-alkylxylene.

`from by distillation. When the olefin used is ethylene,

it may be possible to tolerate large amounts of ethylbenzene in the feed; a suitable feed is the Cs aromatic hydrocarbon fraction obtained by extractive distillation of hydroformate or platformate, i. e., naphtha obtained by the catalytic reforming of virgin naphtha in the presence of hydrogen, which fraction contains about 23% of paraflins and slight amounts of olens and C9 aromatic hydrocarbons.

Liquid xylenes react with BFs and liquid HF to form a complex containing l mol of BFa per mol of xylene and also, probably, 1 mol of HF per mol of xylene. Alkylxylenes also form a complex with BF3 and HF. These complexes are very soluble in liquid HF. lt is necessary in the process that sucient liquid HF be present to dissolve all the complex formed. The presence of liquid HF in excess of this amount is desirable. Thus the amount of liquid HF should be between about 3 mols per mol of xylene present in the feed and about 50* mols. It is preferred to use between about 5 and 20 mols of liquid HF. Put in another way, the amount of liquid HF used may be between about to about 400 volume percent based on xylene charged.

The process must be carried out under substantially anhydrous conditions. The liquid HF used must be substantially anhydrous, that is, the liquid HF should not contain more than about 2-3% of water.

The amount of BFa used in the process may range from about `0.1 mols per mol of xylene (a catalytic amount) 3 to about 5 or more mols. When a mixture of alkylxylene isomers is a satisfactory product, at least about 0.4 mol of BFs per mol of xylene charged should be used.

In order to obtain better yields of alkylate and toobtain a better alkylate product distribution, the process should be operated under conditions wherein essentially all the feed is dissolved into the acid phase. Some BFa and HF may exist in a separate gaseous phase, but it is preferred to operate at a pressure high enough to dissolve essentially all the BF3 in the acid phase. This essentially single homogeneous phase may be obtained by using at least about 1 mol of BF3 per mol of xylene charged, for example, 0.9 mol.

The production of the desired 1,3,5-alkylxylene is favored by the use of enough BF3 to complex all the xylene in the feed. Thus, it is preferred to use between at least 1 and about 3 mols of BF3 per mol of xylene charged, for example, 1.5 mols.

The alkylation of xylene with olefin, in the presence of HIL-BIF;` agent, produces a mixture containing xylene, alkylxyleneY and' polyalkylxylene. The polyalkylate yield may be reduced by operating with an excess of xylene over the amount of olen charged. The mol ratio of xylene to olefin should be at least 1 and a ratio of 20 or more may be used.

With ethylene, itis preferred to use a mol ratio between about 2 and 5, when operating at ordinary atmospheric temperatures, i. e., between about and about +30 C. At higher temperatures, for example, +60 C., the mol ratio may be only slightly in excess of 1, for example 1.03;

The distributionV of alkylxylene isomers and the relative yields of the various alkylate products is dependent upon Vboth the temperature and the time of contacting. It is believed that a mixture of isomers is obtained when the olefin adds to the xylene to form alkylxylene. Following thealkylation reaction, an isomerization reaction occurs in which the 1,3,5-alkylxylene is preferentially formed. Under suitable conditions of time and temperature, essentially all the alkylxylene present in the acid phase will be the 1,3,5-isomer. Shorter contacting times may be used when a high purity 1,3,5-alkylxylene, i. e., about 95%, product fraction is` desired.

The permissible temperatures vary markedly with the type of olefin used in the process. The olefins usable in the process are selected froml the class consisting of ethylene, propylene, isobutylene, butene-l and butene-2. llheuseu of pentenes and higher olefins results in excessive side reactions, such as cracking and rearrangement of the alkyl group. `In order to set out the relationship of temperature and time to product distribution, the various olefins are discussed in accordance withthe individual characteristics of the lalkylate products.

ETHYLENE ALKYLATION ture, is dependent upon the desired degree of conversion of the ethylxylene fraction to the 1,3,5-ethylxylene isomer. Temperatures as low as 20 C. or lower can be used if the correspondingly longer-time of contacting is tolerable; for example, at 20 C., a time of 20 hours sould be used. At about +35 C., a suitable reaction time is about 5 minutes. When using higher ratios ofy xylene to ethylene, the preferred temperature is between about +l5 and +35 C., using a timebetween about 5 minutes and 5 hours, the longer times corresponding to the lower temperatures. Higher temperatures, i. e., +50 to +65 C., have a favorable effect on the yield of ethylxylene at lower xylene to ethylene ratios. Essentially pure 1,3,5-ethylxylene can be produced in very high yield by carrying out the ethylation at about +65 C. for a time of about l0 minutes; at about +50 C., a suitable time is about 30 minutes.

In general, it is preferred to operate with about the minimum contacting time needed to obtain the degree of 1,3,5-ethylxylene readily obtainable at the particular temperature of operation.

PROPYLENE, BUTENE-l AND BUTENE-Z ALKYLATION rThe alkylation of xylene with olefins from the class consisting of propylene, butene-l and butene-2 gives products containing a secondary alkyl group, namely, isopropyl and sec-butyl. VThese secondary alkylxylenes undergo extensive cracking reactions at temperatures above `about +80 C. Condensation reactions proceed to an appreciable extent when long contacting times are used at temperatures of about +40 C. and higher; it is desirable to operate at a temperature of not more than about +40 C.

The secondary alkylxylenes isomerize much more readily than the ethylxylenes; therefore, very low temperatures, such as 20 C., may be employed without having to use extremely long contacting times. At 20 C., high purity 1,3,5-secondary alkylxylene is obtained when using a time of about 2 hours.

As the temperature is raised, the time of contacting is correspondingly decreased. When the temperature of contacting is about +20 C., the contacting time is between about 5 and 20 minutes. At a temperature of +40 C., the time is between about 1 and 5 minutes; at these higher temperatures, the time of contacting should be as short as practicable in order to decrease the yield of side reaction products, i. e., the time should be as close to about l'minute as equipment limitations will permit.

It is preferred to operate the secondary alkylxylene production process at a temperature between about 0 and` +20 C. for a time between about 5 and about 60 minutes, the longer times corresponding to the lower temperatures.

ISOBUTYLENE ALKYLATION The alkylation of xylene with isobutylene gives products containing a tertiary butyl group. These tert-butylxylenes undergo extensive cracking and condensation reactions at temperatures of about '+25 C. In order to substantially avoid these side-reactions, the temperature of operation should be maintained below about +15 C. The yield of the desired 1,3,5-tert-butylxylene is improved by operation at temperatures of not more than about 0 C., for example, 20 C. The tert-butyl group is so active that temperatures as. low as about C. may be used without vrequiring extremely long contacting times.

When operating `at a temperature of about +'15 C., very short contacting times should be used-between about 1 minute and 5 minutes. At 0 C., the contacting time may be between about 5 and 30 minutes. The lower the temperature of contacting, the 4longer the permissible contactingV time, without significant adverse effect on` the yield of the 1,3.,5-tert-butylxylene.

EXAMPLES The results obtainedl by the invention are illustrated by several experimental examples Iand one using HF alone asthe catalysht. The results of these experiments are presented in vTablesI and II. In order to illustrate the experimental procedure, Runs 5 and7 are set out in detail below.

Table I Run No 1 2 3 4 5 6 7 Temperature, C +5 +5 +5 5 +20 +5 +25 Reaction Time, Minutes. 15 15 15 |15 15 15 240 Reaction Mixture:

rn-Xylene, Mols 3.0 3. 3. 0 3.0 3. 02 1. 98 2. 11 p-Xylene, Mols 0.86 0. 92 Ethylbenzene Mols 0.16 Ethylene, M0 s 2.8 2. 7 1. 2 1` 25 1. 21 1. 25 1. 18 Xylene/Ethylene, Mol

Ratio 1.07 l` 11 2. 50 2. 40 2. 50 1 2. 40 2. 57 BF/Xylenes, Mol Ratio Uncorr. 0 0. 75 0. 71 1. 20 1. 50 1 1. 20 1. 50 BFS/Xylenes, Mol Ratio (Corr.) 0 0. 74 0. 70 0. 90 1. 00 0.87 1.00 HF/Xylenes, Mol Ratio. 7. 5 7. 5 7. 5 7. 5 7. 5 7. 5 7. 6

Mols Percent Mols Percent Mols Percent Mols Percent Mols Percent Mols Percent Mols Percent Product Mixture:

1,3,5-Ethy1xy1ene. 1,3,4-Ethylxy1ene. 1,3,2-Ethylxylene. 1,4,3Ethylxylene. C12 Aromatics.

Cw Aromatics 27 36 69 G0 56 G0 G0 48 24 3l 44 40 40 7 18 7 9 0 0 0 51 0 0 0 0 0 0 l rlotal Cs feed.

Table Il Run No 8 9 10 11 12 Temperature, C +15 +60 +60 +15 +5 Time, Minutes 15 60 60 15 30 Reaction Mixture:

m-Xylene,'mols Ethylene, mols.. Propylene, mois. Isobutylene,mols... Xylene/olen, mol ratio. BFa/xylene, mol ratio. HF/xylene, mol ratio Percent Reaction Product Mixture:

RUN 5 The runs were carried out in a 1570 ml. carbon steel autoclave fitted with a 1725 R. P. M. stirrer. 3.02 mols of m-Xylene were added to the reactor; this was followed by 23 mols of liquid HF (150 volume percent on Xylene). BFg was pressured into the reactor from a small cylinder. A total of 4.5 mols of BFS were added, which amounted to an uncorrected BFa/xylene ratio of 1.5. At the reaction temperature of C., the pressure in the reactor was 140 p. s. i. a. Taking into account the free space in the reactor, the partial pressure of HF and the so1ubility of BFS at this temperature and pressure, the free BFS was calculated to be about 1.5 mols. Thus the corrected BFs/Xylene was 1.0, i. e., the the theoretical fo the complexing of all the meta-xylene.

Ethylene gas was added to the contents of the reactor over a period of 5 minutes; 1.21 mols wereadded for a xylene/ethylene ratio of 2.50. The pressure on the reactor indicated the ethylenel was rapidly absorbed.A ,The`

reactor contents were maintained at 20 C. for 15 minutes. The contents were withdrawn into a Dry Ice cooled flask containing about 70 m1, of water. Insofar as could be determined by visual observation, only one single phase homogeneous system had existed in the reactor.

The flask was allowed to warm to room temperature. The contents were transferred to a separating funnel, Where `the supernatant hydrocarbons-displaced from their complexes by the water-were separated from the aqueous acid phase. The hydrocarbons Were Washed with dilute aqueous ammonium hydroxide to remove traces of` HF and BFS. The hydrocarbons were fractionated through a column of 30 theoretical plates. The distillation separated the product into groups according to number of carbon atoms; the composition of each group was determined by a combination of ultraviolet absorption, infrared absorption, refractive index, boiling point and specic gravity.

The total product distribution in this run was as fol- Insof-ar as the analytical methods used could determine, no hydrocarbons containing more than 12 carbon atoms were present in the product.

The properties of the total ethylxyl'ene product in Run and; theproperties of 1,3,5-ethylxylene as given by VBirch et al., JACS, 71, 136,2 (April 1949), are:

Run 5. Birch ct al.

RUN 7 In this run, the feed consisted of 2.11 mols of m-xylene and 0.92 mol of p-xylene. The amount of liquid HF used was 150 volume percent based on total xylene feed. Enough BF3 `was added to. the reactor to give an uncorrected BFa/totalv xylene ratio of 1.5. The pressure in the reactor at the reaction temperature of 25 C. was 160 p. s. i. a. The corrected BFa/total xylene was 1.0, i. e., the theoretical for the complexing of both the metaand para-xylenes.

Ethylene was added to the reactor over a period of 5 minutes; 1.18 mols were added for a total xylene/ ethylene ratio of 2.57. The contents of the reactor were maintained at 25 C. for 4 hours. At the end of this time, the contents of the reactor were withdrawn into a Dry Ice cooled ask containing water. Visual observation of the contents as they were withdrawn indicated the existence of only a single phase homogeneous system.

The reactor contents were handled in the manner de- Vscribed in Run 5. The total product distribution in the Hydrocarbon Percent ni-xyleno The .propertes Ot the. total. ethylxyleneproduct in Run 7 are:l

In Table I, Run 1 showsl the use of liquid HF asthe catalyst for the ethylation of meta-xylene.' In. this run 58% ofV the ethylene reacted to formarornatics containing three or four ethyl groups (C14 and C16 aromatics). Of the ethylxylene produced almost 80% was 1,3,4- ethylxylene which has a methyl group and the ethyl group inV ortho relation. Run Z is substantially identical with Run 1 except that 0.74 (corrected) mols of BFa were added per mol of xylene. In this run no C16 aromatics were produced. The directional-effect ofthe BFsl on the ethylxylene distribution is shown byV the fact that---the-desired 1,3;5-ethylxylene represents about-60%v of thejtotal ethylxylene as against about 5% in Run 1;

Run 5 shows the remarkable improvement obtained in the yield of the desired 1,3,5-ethy1xylene when the amount of BF3 present is sucent to complex all the xylenes so as to form a single phase homogeneous system. This is particularly noteworthy in view of Run 4' where the BF3 was present in an amount only slightly under the theoretical amount; here the ethylxylenes. contained about 30% of 1,3,4-ethylxylene; this effect of the single phase homogeneous system is all the more striking since the amount of ethylxylene produced was about the same in each run.

Runs 6 and 7 used a mixed xylene feed. In Run 6 the paraxylene alkylated to form the 1,4,3-ethylxylene isomer. The ethylbenzene in the feed alkylated to triethylbenzene rather than to diethylbenzene. In Run 7 the 1,4,3-ethy1xylene resulting from the ethylation of para-xylene has been substantially completely isomerized to 1,3,5-ethylxylene; this result is believed to be primarily the effect. of the singlev phase. homogeneous. system. In Run 7 the high disappearance of para-xylene is due to isomerization to the meta isomer, in addition to ethylation.

Runs 9 andv 10 illustrate the effect of high temperature operation on the direction of the ethylation. In Runs 9 and 10 no detectable amounts of any ethylxylene isomer, other than the desired 1,3,5-isomer, were present. In Run 9, 22% of the alkylate was made up of the diand triethylxylenes; in this run slightly less than an equimolar amount of xylene and ethylene was present. However, in Run l0 wherein a slightexcess of xylene was present, only about 6% of the alkylate consists of the diand triethylxylenes. These runs show the marked benelicial effect on yield of the presence of even slight amounts of excess xylene when operating at higher temperatures.

Run 11: illustrates the propylation of m-xylene. The alkylate contained 81% of isopropylxylene-all of which was, within analytical error, the 1,3,5-isopropylxylene isomer. The higher boiling fraction consisted of a wide boiling range mixture of alkylbenzenes and condensation products.

Run 12 illustrates the isobutylation of m-xylene. Herein an appreciable yield of materials believed to be poly-isobutylenes was formedV which is not considered in thereaction product mixture reported. The identifiable alkylate consists of the 1,3,5-tert-butylxylene. Almost an equal quantity of alkylbenzenes and condensa- Vtion products were formed. A shorter time would have increased the yield of the 1,3,5-tert-butylxylene.

ILLUSTRATIVE EMBODIMENT The acompanying drawing shows one embodiment of our process for theproductionof high purity 1,3,5-ethy1- xylene by the ethylation of meta-xylene. It is to be understood that this embodiment is shown for purposes of illustrationonlyl and that many other variations of our process can be readily devised by those skilled in the art.

In this illustration the charge consists of substantially pure meta-xylene from a source 11. However, the charge could be a mixture of meta-xylene, para-xylene and. ethylbenzene, ortho-Xylene or a mixturefof meta, ortho-, paraxyleneand ethylbenzene. Meta-xylene from source 11 is passed through line 12. into line 13. Liquid HF from source 14 is passed through valved line 16, through line 17,V and through line 18 into line13. Thel amount of liquid HF` used here is 10`mols per mol based-on xylene charged. BFa from source 19 is passed through valved line 21, through line 22`and into line 18 where=it is commingled with the liquid. HF. The amount of BF3 used in this example is 1.5 mols of BFa per mol of Xylene chargedin order toinsure the complexing of all xylene charged and the formation-of a single phase homogeneous system. The-liquid HFBF3 in line V18 joins the Xylenei-n lineLv 13 and the whole passes intov mixer 23.V Mixer2'3fmaybe any form ofdevice that provides thorouglragitation; for example;l anzoricefmixer'." The 9 reaction of the BF3, HF and meta-xylene to form the complex is exothermic and mixer 23 is provided with a cooling coil 24 to enable the temperature of the reaction mixture to be controlled.

Ethylene from source 25 is passed through valved line 26 into line 27 Where it meets the homogeneous system passing out of mixer 23. The amount of ethylene used in this example is l mol per 2.5 mols of xylene. Reactor 2S is provided with a coil 29 which is used to maintain the temperature of the reaction mixture relatively constant. Temperature in the reactor in this example is about -{-20 C. The reactants are held in reactor 28 for a time sutiicient to obtain ethylation and conversion of the ethylxylenes into the desired symmetrical 1,3,5- ethylxylene. ln this example, the reaction time is 15 minutes.

From reactor 28 the homogeneous system is passed into line 30 and on into cooler 31. Cooler 31 is needed only when very high reaction temperatures are used; the reaction mixture is cooled quickly in order to eliminate disproportionation of the xylene.

From cooler 31 the mixture is passed through line 32 into stripper 33. In stripper 33 the HF and BFa are removed from the hydrocarbons. In order to avoid the formation of undesirable products through disproportion and cracking, the removal of the HF and BF3 is carried out under vacuum; the stripping operation is facili-- tated by the use of a stripping agent; butane is introduced into stripper 33 through line 34.

The HF and BFS are passed out of stripper 33 through line 36, through vacuum pump 37 and line 38 into condenser 39. In condenser 39 the butane and HF are liquified and are passed through line 41 into settler 42. The free BFS is passed out of settler 42 through lines 43 and 44 to line 22 for reuse in the process. The liquid butane is passed out of settler 42 through line 46 and may be returned to line 34 for reuse in the stripping operation. The liquid HF, saturated with BFs, is passed out of settler 42 through valved line 47 into line 17 and may be reused in the process.

The hydrocarbons are passed out of stripper 33 through line 51 through heater 52 and line 53 into fractionator 54. Fractionator S4 is provided with a reboiler Swhich reboiler in conjunction with heater 52 povides the heat necessary to separate the hydrocarbons into the respective fractions. The unreacted xylene is taken overhead from fractionator 54 through line 56 and is condensed in cooler 57. The xylene is recycled to the reactor by way of valved line 58 and line 59 and line 12.

The ethylxylenes are withdrawn from an upper part of fractionator 54 by way of line 61 and are passed to storage not shown. The ethylxylenes in this example consist of about 95% 1,3,5-ethylxylene and the remainder the 1,3,4- and 1,3,2-ethylxylene configurations.

The higher boiling C12 and any C14 aromatic :fraction is withdrawn from the bottom of fractionator 54 by way of line 6d and are passed to storage, not shown.

One embodiment of the process has been described wherein substantially pure meta-xylene has been the feed material. A mixture of meta-xylene, ortho-xylene and para-xylene can be used with only one variation from the above conditions. For the mixed xylene feed a reaction time of about 2 hours is used in order to isomerize the mixed ethylxylenes to the 1,3,5-ethylxylene.

When the feed to the process contains ethylbenzene, in addition to xylenes, no change in operating conditions need be made. The ethylbenzene reacts to form triethylbenzene and ethylxylene. The triethylbenzene is passed out of the system with the higher boiling C12 and C14 fractions.

When no appreciable demand exists for by-product diethylxylene and triethylxylene, `the process is carried out at higher temperatures. The xylene to ethylene ratio is 1.1 and reactor 28 is maintained at +65 C.; the reaction time is 8 minutes. Essentially pure 1,3,5-ethylxy1ene 10 is withdrawn by way of line 61. In this method of operation, about 95% of the alkylate is the 1,3,5-ethylxylene.

Thus having described the invention, what is claimed 1s:

1. A process for the preparation of mixed. ethylxylenes containing in excess of 1,3,5-ethylxylene which process comprises forming, under substantially anhydrous conditions, an essentially single phase homogeneous sys- `tem consisting essentially of xylene, between about 3 and 50 mols of liquid HF per mol of said xylene, and at least sufficient BF3 to complex substantially all the xylene, adding ethylene to said system in an amount corresponding to between l and 20 mols of xylene per mol of ethylene, maintaining said ethylene containing mixture at a temperature below about 135 C. for a time long enough to obtain the desired ethylxylene product distribution, removing the HF and BFs from the hydrocarbons, and separating the ethylxylenes from said hydrocarbons.

2. The process of claim 1 wherein said xylene consists essentially of a mixture of Cs aromatic hydrocarbons and the usage of said BFa and said liquid HF is based on said mixture.

3. A process for the preparation of high purity 1,3,5- ethylxylene which process comprises forming, under substantially anhydrous conditions an essentially single phase homogeneous system consisting essentially of xylene, between about 5 and 20 mols of liquid HF per mol of said xylene, and at least 1 mol of BFS combined with said xylene to form a liquid HF soluble complex, adding ethylene to said system in the molal ratio of xylene to ethylene between about 2 and 5, maintaining said ethylene containing homogeneous system at a temperature between about +15 C. and +35 C. for a time between about 5 minutes and 5 hours, the longer times corresponding to the lower temperatures, removing the HF and BF?, from the hydrocarbons and separating the ethylxylenes from said hydrocarbons.

4. The process of claim 3 wherein the amount of BFs is between at least 1 and 3 mols per mol of xylene.

5. The process of claim 3 wherein the recovered HF and BF3 are recycled to the reaction system.

6. The process of claim 3 wherein the unreacted xylenes are recycled to the reaction system.

7. A process for the preparation of high purity 1,3,5- ethylxylene, which process comprises (l) contacting under substantially anhydrous conditions, a feed consisting essentially of at least one xylene isomer other than m-Xylene with at least about 1 mol of BFS and between about 3 mols and 50 mols of liquid HF, based on said feed, to form an essentially single phase homogeneous system, (2) adding ethylene to said system in the mol ratio of said feed to ethylene of between about 2 and 5, (3) maintaining said ethylene containing system at between about |15 C. and +35 C. for a time sufficient to attain an ethylxylene containing product, wherein the 1,3,5-ethylxylene isomer represents about of said ethylxylene product, (4) removing HF and BFs from said ethylxylene containing hydrocarbon product, and (5) separating high purity L15-ethylxylene from said product hydrocarbons.

8. The process of claim 7 wherein said feed consists of a mixture of Cs aromatic hydrocarbons.

9. The process of claim 7 wherein said feed is o-xylene.

l0. The process of claim 7 wherein said feed is pxylene.

ll. A process for the preparation of essentially pure 1,3,5-ethylxylene in high yield which process comprises (l) contacting, under substantially anhydrous conditions, a feed consisting essentially of at least one xylene isomer with at least l mol of BFs and between about 3 and 50 mols of liquid HF, respectively per mol of xylene in said feed, to form an essentially single phase homogeneous system, (2) adding ethylene to said system in :a mol ratio of said feed to ethylene of at least about l, while (3) maintaining the reaction zone at a temperature between about +50 and about +65 C. for a time of at least beis between at least 1 and 3 mois and said HF usage is tween about 10 minutes and 30 minutes, the longer minibetween about 5 and 20 mois. mum times corresponding to the lower temperatures, (4) removing HF and BFS from a hydrocarbon product and References Cited in the ie of this patent (5) recovering from said product an ethylxylene fraction 5 t UNITED STATES PATENTS consisting essentially of 1,3,5-ethylxy1ene.

12. The process of claim 11 wherein said feed consists 2,408,753 Burk OGL 3, 1946 essentially of a mixture of Ca aromatic hydrocarbons and 2,521,444 Brooke et al Sept. 5, 1950 said BFs usage i-s 'per mol of Ca aromatics in said feed. 2,563,826 Elwell et al. Aug. 14, 1951 13. The process of claim 11 wherein said BFa usage 2,648,713 Schneider Aug. 11, 1953 

1. A PROCESS FOR THE PREPARATION OF MIXED ETHYLXYLENES CONTAINING IN EXCESS OF 90% 1,3,5-ETHYLXYLENE WHICH PROCCESS COMPRISES FORMING, UNDER SUBSTANTIALLY ANHYDROUS CONDITIONS, AN ESSENTIALLY SINGLE PHASE HOMOGENEOUS SYSTEM CONSISTING ESSENTIALLY OF XYLENE, BETWEEN ABOUT 3 AND 50 MOLS OF LIQUID HF PER MOL OF SAID XYLENE, AND AT LEAST SUFFICIENT BF3 TO COMPLEX SUBSTANTIALLY ALL THE XYLENE, ADDING ETHYLENE TO SAID SYSTEM IN AN AMOUNT CORRESPONDING TO BETWEEN 1 AND 20 MOLS OF XYLENE PER MOL OF ETHYLENE, MAINTAINING SAID ETHYLENE CONTAINING MIXTURE AT A TEMPERATURE BELOW ABOUT 135* C. FOR A TIME LONG ENOUGH TO OBTAIN THE DESIRED ETHYLXYLENE PRODUCT DISTRIBUTION, REMOVING THE HF AND BF3 FROM THE HYDROCARBONS, AND SEPARATING THE ETHYLXYLENES FROM SAID HYDROCARBONS. 